The present invention relates to catheter tracking systems, which operate to determine a position of a catheter within the human or animal body.
Furthermore, the invention relates to a method for tracking a catheter within the human or animal body.
Electro-cardiography is a process for recording electrical signals created by a heart, using electrodes applied externally and, more particularly, electrodes positioned on tips of catheters inserted within the heart. In known endocardial catheter technology great use is made of in-theatre fluoroscopy to locate and guide the catheters to positions within the heart where measurements are required. The use of fluoroscopy has a disadvantage that inevitably theatre staff and the patient are exposed to X-ray radiation.
In order to circumvent this disadvantage, an endocardial catheter tracking system has been recently proposed, in which an AC magnetic field generated by a set of three coils mounted below the patient within the structure of a theatre table is used to track a tip of a catheter provided with a magnetic sensor. The system is complicated by the fact that the patient may move on the table and thus destroy the accuracy in the measurement of the position of the catheter tip relative to the heart. In order to overcome this problem a further catheter is used which also carries a magnetic sensor. This catheter is referred to as a reference catheter. The catheter tracking system is arranged to sense the position of the reference catheter and thereafter to determine the position of the measurement catheter. To this end, the reference catheter must be fixed somewhere in or near the heart in such a way so as to maintain its position relative to the heart. For example, this might be inserted in the coronary sinus or the right ventricular apex. The coronary sinus is a small blood vessel that has its entrance in the auricle close to the inferior vena cava and the entrance to the right ventricle. The coronary sinus is of varying diameter but can be as much as 10 mm. The right ventricular apex is an area at the lower end of the right ventricle in the base of the heart. It is not a well-defined location and does not offer a very good fixing position for the reference catheter. As a result of a possible range of movement of the reference catheter, the known arrangement of reference and measurement catheters provides difficulties in positioning the measurement catheter accurately, in particular when in actual use in the heart.
Furthermore, the use of an additional catheter increases a risk of infections and renders the use of this known tracking system cumbersome.